1. Field of the Invention
Embodiments of the present invention generally relate to valves for use in wellbores.
2. Description of the Related Art
Subsequent to the drilling of an oil or gas well, the well is completed by running into such well a string of casing which is cemented in place. Thereafter, the casing is perforated to permit the fluid hydrocarbons to flow into the interior of the casing and subsequently to the top of the well. Such produced hydrocarbons are transmitted from the production zone of the well through a production tubing or work string which is concentrically disposed relative to the casing.
In many well completion operations, it frequently occurs that it is desirable, either during the completion, production, or workover stages of the life of the well, to have fluid communication between the annular area between the interior of the casing and the exterior of the production tubing or workstring with the interior of such production tubing or workstring for purposes of, for example, injecting chemical inhibitor, stimulants, or the like, which are introduced from the top of the well through the production tubing or workstring and to such annular area. Alternatively, it may be desirable to provide such a fluid flow passageway between the tubing/casing annulus and the interior of the production tubing so that actual production fluids may flow from the annular area to the interior of the production tubing, thence to the top of the well. Likewise, it may be desirable to circulate weighting materials or fluids, or the like, down from the top of the well in the tubing/casing annulus, thence into the interior of the production tubing for circulation to the top of the well in a “reverse circulation” pattern.
In instances as above described, it is well known in the industry to provide a well tool having a port or ports therethrough which are selectively opened and closed by means of a sliding sleeve element positioned interiorly of the well tool. Such sleeve typically may be manipulated between open and closed positions by means of wireline, remedial coiled tubing, electric line, or any other well known auxiliary conduit and tool means. In some tools, it is desirable to provide intermediate positions between the open and closed positions so that flow through the tool may be regulated. One way to accomplish this is to mismatch the slots in the sleeve with the port(s) in the housing. Another way is to configure the sleeve with a plurality of different sized slots and to configure the tool so that the different slots may be selectively aligned with the port in the housing.
Typically, in tools having the multi-sized slots, the tool must contain some sort of elastomeric or metallic sealing element used to isolate the port and currently aligned slot from the rest of the slots and the tool. This same sealing element is also used to isolate the slots form the port when the tool is in a closed position. Thus, if the sealing element should fail, the tool cannot be effectively closed. Further, such failure could adversely affect the sealing integrity of the entire production tubing conduit.
Typically, in tools configured to regulate flow by mismatching the slots in the sleeve with the port(s) in the housing, a series of upper and lower primary seals are placed in the housing for dynamic sealing engagement relative to the exterior of the sleeve which passes across the seals during opening and closing of the port element. As with all seals, such primary sealing means also represent an area of possible loss of sealing integrity.
Accordingly, there is a need for a variable choke flow control tool with a seal configuration which is more reliable, thereby reducing the chances of loss of sealing integrity through the tool and the tubular conduit.